The present invention relates to an apparatus and a method for estimating the level of wakefulness of a driver from displacements of the vehicle body in a lateral direction thereof.
The development of techniques for preventing accidents attributable to a reduction in the wakefulness of drivers is one of important subjects from the viewpoint of safety, and various methods for detecting a reduction of wakefulness and alarming techniques associated therewith have been conceived and put in use.
In JP-A-2002-154345, the applicant has proposed a technique associated with estimation of wakefulness for allowing the level of wakefulness of a driver to be accurately determined in the presence of significant changes in the driving environment and vehicle speed.
According to the wakefulness estimating technique disclosed in JP-A-2002-154345, displacements of a vehicle in the width direction of the vehicle are detected at first as a time series; the displacements are subjected to frequency transformation to calculate the quantities of frequency power components; and an average value of the quantities of frequency power components is calculated as the quantity of high frequency components. At the same time, a maximum value of the quantities of frequency power components within a predetermined frequency range including a stagger frequency exposed when the driver is at a low level of wakefulness is calculated as the quantity of low frequency components.
Then, the level of wakefulness of the driver is determined based on the ratio of the quantity of high frequency components to the quantity of low frequency components.
According to JP-2002-154345, the wakefulness of a driver is determined to be low when the quantity of high frequency components is small and the quantity of the low frequency components is great.
However, wakefulness is not instantaneously determined, but a reduction in the level of wakefulness or the like is estimated by comparing a phenomenon of a certain level that has appeared with a threshold.
In general, a wakefulness estimating apparatus of this type issues an alarm as soon as a reduction in the level of wakefulness is determined to warn the driver. However, the timing of such an alarm is not stable, which lets a driver feel uncomfortable.
An active driver assist system (ADA) recognizes left and right lane markings located ahead the vehicle in the traveling direction thereof based on an image obtained by a camera loaded on the vehicle and issues an alarm to warn the driver when the vehicle deviates from the lane markings.
However, it is difficult for a driver at a low level of wakefulness to properly perform an avoiding operation when an alarm is issued at the time of a deviation from a lane marker (a white line).